There is an actual book of secrets buried in "National Treasure: Book of Secrets," and it's not nearly as musty as the script.

There is an actual book of secrets buried in “National Treasure: Book of Secrets,” and it’s not nearly as musty as the script. Graced with some extra star wattage courtesy of Helen Mirren and Ed Harris, this diminishing-returns sequel sends Nicolas Cage on another quest to strike it rich, get young auds excited about history and solve puzzles that are generally less stimulating than yesterday’s Sudoku. The 2004 original grossed a surprising $347 million worldwide; with little change to the formula and even more marketing muscle, Disney and producer Jerry Bruckheimer should see their B.O. and homevid coffers flooded anew.

The first “National Treasure” was not without its charms — namely, an endearingly geeky obsession with clues and codes and a polite aversion to the explosive violence typical of most Bruckheimer-produced actioners. This time around, however, the riddles are conspicuously less clever, the humor more obvious, the stabs at educational value even more perfunctory. Sorry, but having a character tearfully marvel at how the discovery of an ancient city of gold will revolutionize the study of pre-Columbian artifacts doesn’t qualify as deep engagement with history.

Opening flashback to President Lincoln’s assassination on April 14, 1865, establishes the heroic legacy of Thomas Gates (Joel Gretsch), who was murdered that same evening by a shadowy society of Confederate treasure-hunters. Back in the present day, one Mitch Wilkinson (Harris), so dastardly he speaks with a Southern accent, comes forth with evidence that Gates actually masterminded Lincoln’s killing. It’s up to professional nerd Ben Gates (Cage) and dad Patrick (Jon Voight) to clear their ancestor’s name — and find the missing gold.

Along the way, the Gateses must endure tiresome comic relief (Justin Bartha, back as tech whiz Riley) and reconcile with their estranged exes — Ben with blonde bombshell/documents expert Abigail (Diane Kruger), and Patrick with Ben’s short-tempered mom, Emily (a plucky Mirren), a professor conveniently well-versed in Native American languages. Soon they’re trotting the globe, tearing up cities in high-speed car chases, ransacking national landmarks for hints and exploring subterranean caverns, like the stars of a poor man’s “Bourne Ultimatum,” “Indiana Jones” and “The Da Vinci Code” all rolled into one.

The characters here don’t just solve ciphers; they are ciphers, their dialogue and emotional interactions no less mechanical than all the secret switches and hidden compartments (left for them to discover by long-deceased puzzlemeisters who clearly had too much time on their hands). Sole exception is Bruce Greenwood, exuding his usual gravitas as a fictive U.S. president — an honorable figure who typifies the film’s fuzzy nostalgia for simpler, more patriotic times.

With producer-director Jon Turteltaub back at the helm (pic’s five exec producers include original story creators Oren Aviv and Charles Segars), tech package is OK, with flat, functional lensing and nicely underplayed visual effects. Pic’s impressive world tour includes stops in Paris, London and Washington, D.C., en route to a climax at Mount Rushmore that won’t give “North by Northwest” a run for its money. Product placements are much more assaultive than the action scenes.